The present invention relates to a gearbox casing, and more particularly, to a gearbox casing for an epicyclic change-speed gearbox, comprising two casing wall parts branching off upwards from a base part open towards the bottom in an installed position and arranged on both sides of a casing longitudinal axis coinciding with a central main axis of rotation of the rotating gearbox parts and extending in the directions of the casing longitudinal axis so as to enclose therebetween a casing interior accommodating rotating gearbox parts of the epicyclic change-speed gearbox and form a unitary cylindrical casing outer part, and a casing inner part is arranged in the casing interior in a rotationally fixed manner relative to the base part and extends partially between a lower portion of the outermost orbit of the rotating gearbox parts and one region of the casing interior enclosed by the base part. The casing inner part is configured as an intermediate wall extending from one of the two casing wall parts to the other of the two casing wall parts branching off upwards from the base part and to partition off another region of the casing interior which accommodates the rotating gearbox parts from the one region of the casing interior enclosed by the base part and is open towards the bottom, the casing inner part being cylindrical and lying centrally with respect to the casing longitudinal axis. The casing outer part and the casing inner part constitute a one-piece casing cylinder, and at least one outlet opening for lubricating oil is arranged to connect the another region of the casing interior which accommodates the rotating gearbox parts to the downwardly open region of the casing interior. One wall surface of the casing cylinder contains an inner mouth of the outlet opening, said mouth lying in the another region of the casing interior which accommodates the rotating gearbox parts.
DE 30 21 162 A1 discloses a gearbox casing in which two slot-shaped outlet openings extending in the circumferential direction of the main axis of rotation are provided in the cylindrical casing inner part used as an intermediate wall at a point which is at the smallest distance from the base end surface which closes off the base part at the bottom in the installed position, i.e. are situated in that section of the wall of the casing cylinder which is at the lowest point in the installed position. As a result, even when travelling at constant speed on the flat, oil can enter that region of the casing interior which accommodates the rotating gearbox parts, i.e. the casing cylinder, from the oil pan via the outlet openings situated at the bottom, especially when the oil heats up and its volume increases. DE 29 37 501 A1 discloses the installation of a gear train in the case of a gearbox casing of the type described in DE 30 21 162 A1.
DE 38 06 996 C2 discloses a gearbox casing which is to be installed transversely in the direction of travel of a motor vehicle. For the accommodation of a component belonging to a gearwheel set and rotating in an oil-lubricated support, the casing is provided with a casing intermediate wall which partially divides the space between the rotating component, the gearwheel set and the front casing outer wall into an annular segment-like space between the rotating component, the gearwheel set and the casing intermediate wall and into an oil return duct between the casing intermediate wall and the casing outer wall. The end of the casing intermediate wall which is at the top in the installed position of the gearbox casing defines the inlet opening of the oil return duct above the rotating component of the gearwheel set, and the lower end defines the outlet opening, open towards the oil pool, below the rotating component of the gearwheel set.
Given this special arrangement and configuration of the casing intermediate wall to create an oil return duct, the gearbox casing is said to have an excellent lubricant cooling capacity. The lubricant thrown off from the rotating component by centrifugal force due to its rotation is intended to be guided into the oil return duct at the inlet opening above the rotating component. The lubricant picked up by the rotating component, which is stirred up in the oil pool, is supposed to spray off due to the centrifugal force while it is being taken upwards by the rotating component. Consequently, the majority of the lubricant is guided from the inlet opening into the oil return duct. The lubricant introduced into this duct is supposed to flow in the latter towards the outlet opening and drip from the latter into the oil pool. The result of this is intended to be that the lubricant sprayed off by the rotating component is prevented from dripping onto the rotating component again before it returns to the oil pool. Because, furthermore, the oil return duct is arranged at the front end of the vehicle, the lubricant flowing through this duct is supposed to be cooled in an effective manner by the impinging relative wind.
An object on which the present invention is based is essentially to prevent lubricant from passing out of the oil sump, generally provided underneath the base part of the gearbox casing in the form of an oil pan, via the downwardly open gearbox casing to the rotating gearbox parts when the oil level rises, for example due to temperature effects, dynamic driving states or an oblique position of the vehicle.
The foregoing object has been achieved in an advantageous manner by the present invention, with a wall surface containing the inner mouth lying on a casing bulge which is bounded opposite the casing interior, by an inner wall surface, starting from a point on the cylindrical inner wall of the cylindrical casing outer part lying ahead of the mouth in relation to a forward rotation direction of the rotating gearbox parts to follow a spiral course away from the casing longitudinal axis in a circumferential direction of the central axis of rotation corresponding to the forward rotation direction.
In the above-described gearbox casing according to the present invention, the upper region of the casing interior, which upper region accommodates the rotating gearbox parts, is partitioned off from the lower region of the casing interior, which region generally accommodates shifting and control apparatus for the hydraulic shift actuators and is open towards the oil pool, with the result that oil cannot cross from the oil pool to the rotating gearbox parts.
In the gearbox casing according to the present invention, not only is a compact construction achieved but, in particular, it is also ensured that all the rotating gearbox parts accommodated in the upper region are partitioned off from the oil pool. Further, a circulating oil film consisting of the oil particles thrown off by the rotating gearbox parts is formed on the cylindrical casing inner wall, thereby preventing a large part of the oil used for lubrication from dripping back onto the rotating gearbox parts after flowing through the latter.
In the gearbox casing according to the present invention, the lubricating oil is fed to the lubrication points in a known manner via oil passages in the gearbox shafts. The lubricating oil is diverted into the oil pool after leaving the lubrication points via the oil outlets in the casing bulge.
Other advantageous arrangements and configurations of the outlet opening are adapted to the conditions of an oil film circulating on the cylindrical inner wall of the gearbox casing according to the present invention.
To avoid a situation, with the gearbox casing according to the invention, where the oil pump which is generally arranged in the oil pan mounted on the casing base part from below can suck in air because the oil level is too low, an oil level-safeguarding valve is provided and this can be arranged and controlled in an advantageous manner, for example, as a function of at least one operating parameter associated with the supply of pressure oil and lubricating oil.